48 THE OPEN BOOK OF NATURE 
have got beyond recognition. In the upper Archzan 
rocks there are traces of life. Seams of limestone 
therein may have been organically formed, and some 
graphite has been found, which may be greatly 
altered seaweeds. The Torridon Sandstone of the 
North-West Highlands of Scotland has yielded some 
grains of phosphate, which seem to be organic in 
nature. 
Let us proceed with our table (see p. 49). 
THe Pataozoic ERA. 
It will be interesting for you to have some reasons 
for the names given to the Periods of the Paleozoic 
Era. The name “ Cambrian ” comes from Cambria, 
the old name given to Wales, where the Cambrian 
rocks are typically developed. ‘‘ Ordovician ”’ rocks 
appear typically in the country once occupied by the 
tribe called Ordovices, in Shropshire and Kast Wales. 
The Stlures, who in Roman times held part of Shrop- 
shire, also Central and South Wales, have the 
“Silurian” rocks named after them. The term 
‘* Devonian ” comes from Devonshire, where these 
rocks were first studied. ‘Carboniferous ’’ comes 
from carbo =coal, and the name is given on account 
of the Coal Measures which are conspicuous in the 
rocks of the Period. ‘‘ Permian ” relates to the 
province of Perm, in Russia, where the rocks are 
typical. 
The fossils of the Paleozoic Era are largely the 
remains of families, orders, genera, and species of 
creatures that are now extinct. The Trilobites, of 
which I shall have more to say, existed from Cam- 
brian to Permian times, when they seem to have 
